Ricci-flat and Einstein pseudoriemannian nilmanifolds

This is partly an expository paper, where the authors' work on pseudoriemannian Einstein metrics on nilpotent Lie groups is reviewed. A new criterion is given for the existence of a diagonal Einstein metric on a nice nilpotent Lie group. Classifications of special classes of Ricci-flat metrics on nilpotent Lie groups of dimension $\leq8$ are obtained. Some related open questions are presented.Comment: 30 pages, 1 figure. v2: added a comment on a recent example of an Einstein nilpotent Lie algebra of dimension 7; added a remark and a question concerning the characteristically nilpotent case; replaced the "\sigma-compatible" condition with the more general "\sigma-diagonal"; added 3 reference

A Survey on Industrial Control System Testbeds and Datasets for Security Research

The increasing digitization and interconnection of legacy Industrial Control Systems (ICSs) open new vulnerability surfaces, exposing such systems to malicious attackers. Furthermore, since ICSs are often employed in critical infrastructures (e.g., nuclear plants) and manufacturing companies (e.g., chemical industries), attacks can lead to devastating physical damages. In dealing with this security requirement, the research community focuses on developing new security mechanisms such as Intrusion Detection Systems (IDSs), facilitated by leveraging modern machine learning techniques. However, these algorithms require a testing platform and a considerable amount of data to be trained and tested accurately. To satisfy this prerequisite, Academia, Industry, and Government are increasingly proposing testbed (i.e., scaled-down versions of ICSs or simulations) to test the performances of the IDSs. Furthermore, to enable researchers to cross-validate security systems (e.g., security-by-design concepts or anomaly detectors), several datasets have been collected from testbeds and shared with the community. In this paper, we provide a deep and comprehensive overview of ICSs, presenting the architecture design, the employed devices, and the security protocols implemented. We then collect, compare, and describe testbeds and datasets in the literature, highlighting key challenges and design guidelines to keep in mind in the design phases. Furthermore, we enrich our work by reporting the best performing IDS algorithms tested on every dataset to create a baseline in state of the art for this field. Finally, driven by knowledge accumulated during this survey's development, we report advice and good practices on the development, the choice, and the utilization of testbeds, datasets, and IDSs

Vita activa and lex naturae in Chromatius of Aquileia: the case of Sermo III

The Sermones of Chromatius of Aquileia offer us direct evidence of his episcopal and literary experience, divided between the most marked exegesis and the pastoral objective. The structural and linguistic simplicity and the reference to a few contemporary authors, characteristics of the third of these homiletic compositions, offer us the opportunity to analyse the most intimate and practical purposes of this text. The close relationship with the audience, in fact, and the intent to guide them on a right Christian path are evident protagonists in the flow of the entire sermon. At the same time, however, the scriptural exegesis of Chromatius and his doctrinal study run: the Bishop tries to offer a small baggage useful to the path of those who listen to him, in a strong enhancement of human action. The vita activa adhering to the lex naturae inherent in the human soul constitutes, in fact, the most evident theme of the entire homily, expounded by the Aquileian above all with the aim of strengthening the unity and the identity of the listeners in the face of external pressures. Above all, the scriptural reference is strong, present throughout the Sermo: the passage, certainly read just before the exposition, is almost entirely reported, and exposed to the faithful, so as to make it more fixed in the memory of those who attend.Los Sermones de Cromacio de Aquilea nos ofrecen evidencia directa de su experiencia episcopal y literaria, que se divide entre la exégesis más destacada y el objetivo pastoral. La simplicidad estructural y lingüística, y la referencia a algunos autores contemporáneos, características de la tercera de estas composiciones homiléticas, nos ofrecen la oportunidad para analizar los propósitos más íntimos y prácticos de este texto. De hecho, la estrecha relación con su audiencia y el intento de guiarla por el justo camino cristiano son los evidentes protagonistas en todo el discurrir del sermón. Sin embargo, al mismo tiempo se observa también la exégesis escritural de Cromacio y su profundización doctrinal: el Obispo trata de ofrecer un pequeño pero útil bagaje para el camino de quien lo escucha, en una poderosa valorización de la acción humana. La vita activa que se suma a la lex naturae inherente al alma humana constituye, de hecho, el tema más evidente de la homilía íntegra, que expone el de Aquilea sobre todo con el objetivo de fortalecer la unidad y la identidad de quienes escuchan cuando enfrentan presiones externas. La referencia escritural es fuerte y está presente en todo el sermón: el pasaje, seguramente leído justo antes de la exposición, se expone casi en su totalidad a los fieles, para fijarlo mejor en la memoria de aquellos que asisten a la lectura